Group 16 elements, also known as the chalcogens, typically form ions with a charge of -2. This is because these elements, which include oxygen, sulfur, selenium, tellurium, and polonium, have six valence electrons.
When they react, these elements tend to gain two electrons to achieve a stable octet configuration, similar to the nearest noble gas. This electron gain results in the formation of anions with a -2 charge. For instance, when oxygen gains two electrons, it becomes an oxide ion (O2-).
In summary, the chalcogens generally form ions with a -2 charge due to their desire to complete their outer electron shell for increased stability.